1. Field Of The Invention
This invention relates to an automatic car-speed controller used for controlling the traveling speed of a car at a set point automatically.
2. Description Of The Prior Art
Heretofore, there have been many types of such automatic car-speed controllers. Among them, there has been an automatic car-speed controller disclosed in Japanese Patent Disclosure (Kokai) No. 61-287830/86, for example.
Said automatic car-speed controller has a construction comprising a car-speed sensor for outputting operating data proportional to an actual car-speed, a command switch for outputting a cruise command signal, a car-speed memorizing means for memorizing the operating data from said car-speed sensor in response to an operation of said command switch, a motor driven actuator for opening and closing a throttle by rotation of a driving motor through an electromagnetic clutch, a driving circuit for rotating the driving motor of said actuator in the forward and reverse directions, and a control means for giving a command to said driving circuit corresponding to a difference between actual car-speed and memorized car-speed in a state in which the electromagnetic clutch is excited at the time of an automatic car-speed control and for making the electromagnetic clutch into a deenergized state after rotating the driving motor to the full-closed position of the throttle at the time of cancelling the automatic car-speed control.
In said automatic car-speed controller, the memorizing means memorizes the car-speed at the time of OFF-operation by setting of a setting switch of the command switch subsequent to the ON-operation of the setting switch, the control means makes the electromagnetic clutch of the actuator into the excited state and gives the command to the driving circuit corresponding to the difference between actual car-speed and memorized car-speed. According to the command from said control means the driving circuit opens or closes the throttle by rotating the driving motor of the actuator, thereby the actual car-speed is controlled to the memorized car-speed so as to travel at a constant speed. When the automatic car-speed control is canceled by working a brake pedal or the like, the control means makes the electromagnetic clutch into a deenergized state after rotating the driving motor to the full-closed position of the throttle, said throttle is returned to the full-closed position at all times by the rotation of the driving motor through the electro magnetic clutch.
However, in the conventional automatic car-speed controller described above, because the electromagnetic clutch is always made into unexcited state after returning the driving motor of the actuator to the full-closed position of the throttle at the time of cancelling the automatic car-speed control in order to make sure of safety of the system from troubles in the electromagnetic clutch whether the electromagnetic clutch of the actuator is normal or not, the time is required in some measure for returning the driving motor to the full-closed position of the throttle. Thus, there is a problem since it is impossible to cancel rapidly the automatic car-speed control. There is another problem in that it is not improbable that the automatic car-speed controller is operated at a state in which the electromagnetic clutch breaks down.